This invention pertains to fused abrasive particles comprised of Al2O3xe2x80x94MgO-rare earth oxide eutectic materials and methods of making the same. The fused abrasive particles can be incorporated into a variety of abrasive articles, including bonded abrasives, coated abrasives, nonwoven abrasives, and abrasive brushes.
There are a variety of abrasive particles (e.g., diamond particles, cubic boron nitride particles, fused abrasive particles, and sintered, ceramic abrasive particles (including sol-gel-derived abrasive particles) known in the art. In some abrading applications, the abrasive particles are used in loose form, while in others the particles are incorporated into abrasive products (e.g., coated abrasive products, bonded abrasive products, non-woven abrasive products, and abrasive brushes). Criteria used in selecting abrasive particles used for a particular abrading application include: abrading life, rate of cut, substrate surface finish, grinding efficiency, and product cost.
From about 1900 to about the mid-1980""s, the premier abrasive particles for abrading applications such as those utilizing coated and bonded abrasive products were typically fused abrasive particles. There are two general types of fused abrasive particles: (1) fused alpha alumina abrasive particles (see, e.g., U.S. Pat. No. 1,161,620 (Coulter), U.S. Pat. No. 1,192,709 (Tone), U.S. Pat. No. 1,247,337 (Saunders et al.), U.S. Pat. No. 1,268,533 (Allen), and U.S. Pat. No. 2,424,645 (Baumann et al.)) and (2) fused (sometimes also referred to as xe2x80x9cco-fusedxe2x80x9d) alumina-zirconia abrasive particles (see, e.g., U.S. Pat. No. 3,891,408 (Rowse et al.), U.S. Pat. No. 3,781,172 (Pett et al.), U.S. Pat. No. 3,893,826 (Quinan et al.), U.S. Pat. No. 4,126,429 (Watson), U.S. Pat. No. 4,457,767 (Poon et al.), and U.S. Pat. No. 5,143,522 (Gibson et al.))(also see, e.g., U.S. Pat. No. 5,023,212 (Dubots et. al) and U.S. Pat. No. 5,336,280 (Dubots et.al) which report the certain fused oxynitride abrasive particles). Fused alumina abrasive particles are typically made by charging a furnace with an alumina source such as aluminum ore or bauxite, as well as other desired additives, heating the material above its melting point, cooling the melt to provide a solidified mass, crushing the solidified mass into particles, and then screening and grading the particles to provide the desired abrasive particle size distribution. Fused alumina-zirconia abrasive particles are typically made in a similar manner, except the furnace is charged with both an alumina source and a zirconia source, and the melt is more rapidly cooled than the melt used to make fused alumina abrasive particles. For fused alumina-zirconia abrasive particles, the amount of alumina source is typically about 50-80 percent by weight, and the amount of zirconia, 50-20 percent by weight zirconia. The processes for making the fused alumina and fused alumina abrasive particles may include removal of impurities from the melt prior to the cooling step.
Although fused alpha alumina abrasive particles and fused alumina-zirconia abrasive particles are still widely used in abrading applications (including those utilizing coated and bonded abrasive products, the premier abrasive particles for many abrading applications since about the mid-1980""s are sol-gel-derived alpha alumina particles (see, e.g., U.S. Pat. No. 4,314,827 (Leitheiser et al.), U.S. Pat. No. 4,518,397 (Leitheiser et al.), U.S. Pat. No. 4,623,364 (Cottringer et al.), U.S. Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.), U.S. Pat. No. 4,881,951 (Wood et al.), U.S. Pat. No. 4,960,441 (Pellow et al.), U.S. Pat. No. 5,139,978 (Wood), U.S. Pat. No. 5,201,916 (Berg et al.), U.S. Pat. No. 5,366,523 (Rowenhorst et al.), U.S. Pat. No. 5,429,647 (Larmie), U.S. Pat. No. 5,547,479 (Conwell et al.), U.S. Pat. No. 5,498,269 (Larmie), U.S. Pat. No. 5,551,963 (Larmie), and U.S. Pat. No. 5,725,162 (Garg et al.)).
The sol-gel-derived alpha alumina abrasive particles may have a microstructure made up of very fine alpha alumina crystallites, with or without the presence of secondary phases added. The grinding performance of the sol-gel derived abrasive particles on metal, as measured, for example, by life of abrasive products made with the abrasive particles was dramatically longer than such products made from conventional fused alumina abrasive particles.
Typically, the processes for making sol-gel-derived abrasive particles are more complicated and expensive than the processes for making conventional fused abrasive particles. In general, sol-gel-derived abrasive particles are typically made by preparing a dispersion or sol comprising water, alumina monohydrate (boehmite), and optionally peptizing agent (e.g., an acid such as nitric acid), gelling the dispersion, drying the gelled dispersion, crushing the dried dispersion into particles, screening the particles to provide the desired sized particles, calcining the particles to remove volatiles, sintering the calcined particles at a temperature below the melting point of alumina, and screening and grading the particles to provide the desired abrasive particle size distribution. Frequently a metal oxide modifier(s) is incorporated into the sintered abrasive particles to alter or otherwise modify the physical properties and/or microstructure of the sintered abrasive particles.
There are a variety of abrasive products (also referred to xe2x80x9cabrasive articlesxe2x80x9d) known in the art. Typically, abrasive products include binder and abrasive particles secured within the abrasive product by the binder. Examples of abrasive products include: coated abrasive products, bonded abrasive products, nonwoven abrasive products, and abrasive brushes.
Examples of bonded abrasive products include: grinding wheels, cutoff wheels, and honing stones). The main types of bonding systems used to make bonded abrasive products are: resinoid, vitrified, and metal. Resinoid bonded abrasives utilize an organic binder system (e.g., phenolic binder systems) to bond the abrasive particles together to form the shaped mass (see, e.g., U.S. Pat. No. 4,741,743 (Narayanan et al.), U.S. Pat. No. 4,800,685 (Haynes et al.), U.S. Pat. No. 5,038,453 (Narayanan et al.), and U.S. Pat. No. 5,110,332 (Narayanan et al.)). Another major type are vitrified wheels in which a glass binder system is used to bond the abrasive particles together mass (see, e.g., U.S. Pat. No. 4,543,107 (Rue), U.S. Pat. No. 4,898,587 (Hay et al.), U.S. Pat. No. 4,997,461 (Markhoff Matheny et al.), and U.S. Pat. No. 5,863,308 (Qi et al.)). These glass bonds are usually matured at temperatures between 900xc2x0 C. to 1300xc2x0 C. Today vitrified wheels utilize both fused alumina and sol-gel-derived abrasive particles. However, fused alumina-zirconia is generally not incorporated into vitrified wheels due in part to the thermal stability of alumina-zirconia. At the elevated temperatures at which the glass bonds are matured, the physical properties of alumina-zirconia degrade, leading to a significant decrease in their abrading performance. Metal bonded abrasive products typically utilize sintered or plated metal to bond the abrasive particles.
The abrasive industry continues to desire abrasive particles and abrasive products that are easier to make, cheaper to make, and/or provide performance advantage(s) over conventional abrasive particles and products.
The present invention provides a fused, crystalline abrasive particle comprising (preferably, at least 20, 30, 40, 50, 60, 70, 75, 80, 85, 90, 95, 98, 99, or 100 percent by volume, based on the total metal oxide volume of the particle) eutectic material, wherein the eutectic material comprises eutectic of at least crystalline, complex Al2O3xe2x80xa2MgO and crystalline, complex Al2O3xe2x80xa2rare earth oxide. Preferably, a fused, crystalline abrasive particle according to the present invention comprises, on a theoretical oxide basis, at least 30 percent (or even at least 40, 50, 60, 70, or 80 percent) by weight Al2O3, based on the total metal oxide content the particle.
In another aspect, the present invention provides a plurality of particles having a particle size distribution ranging from fine to coarse, wherein at least a portion of the plurality of particles are fused, crystalline abrasive particles according to the present invention.
In this application:
xe2x80x9csimple metal oxidexe2x80x9d refers to a metal oxide comprised of a one or more of the same metal element and oxygen (e.g., Al2O3, CeO2, MgO, SiO2, and Y2O3);
xe2x80x9ccomplex metal oxidexe2x80x9d refers to a metal oxide comprised of two or more different metal elements and oxygen (e.g., CeAl11O18, Dy3Al5O12, MgAl2O4, and Y3Al5O12);
xe2x80x9ccomplex Al2O3xe2x80xa2metal oxidexe2x80x9d refers to a complex metal oxide comprised of, on a theoretical oxide basis, Al2O3 and one or more metal elements other than Al (e.g., CeAl11O18, Dy3Al5O12, MgAl2O4, and Y3Al5O12);
xe2x80x9ccomplex Al2O3xe2x80xa2Y2O3xe2x80x9d refers to a complex metal oxide comprised of, on a theoretical oxide basis, Al2O3 and Y2O3 (e.g., Y3Al5O12);
xe2x80x9ccomplex Al2O3xe2x80xa2rare earth oxidexe2x80x9d or xe2x80x9ccomplex Al2O3xe2x80xa2REOxe2x80x9d refers to a complex metal oxide comprised of, on a theoretical oxide basis, Al2O3 and rare earth oxide (e.g., CeAl11O18 and Dy3Al5O12);
xe2x80x9crare earth oxidesxe2x80x9d refer to, on a theoretical oxide basis, CeO2, Dy2O3, Er2O3, Eu2O3, Gd2O3, Ho2O3, La2O3, Lu2O3, Nd2O3, Pr6O11, Sm2O3, Th4O7, Tm2O3, and Yb2O3;
xe2x80x9cREOxe2x80x9d means rare earth oxide;
and
xe2x80x9cparticle sizexe2x80x9d is the longest dimension of a particle.
In another aspect, the present invention provides a method for making fused, crystalline abrasive particles according to the present invention, the method comprising:
melting at least one Al2O3 source, at least one MgO source, and at least one rare earth oxide source to provide a melt; and
converting the melt to the fused, crystalline abrasive particles.
Fused abrasive particles according to the present invention can be incorporated into various abrasive products such as coated abrasives, bonded abrasives, nonwoven abrasives, and abrasive brushes.
The present invention also provides a method of abrading a surface, the method comprising:
contacting at least one fused abrasive particle according to the present invention (preferably, a plurality of fused abrasive particles according to the present invention) with a surface of a workpiece; and
moving at least of one the fused abrasive particle according to the present invention or the surface relative to the other to abrade at least a portion of the surface with the fused abrasive particle according to the present invention.
Preferred fused abrasive particles according to the present invention provide superior grinding performance as compared to conventional fused abrasive particles. Preferred fused abrasive particles according to the present invention are sufficiently microstructurally and chemically stable to allow them to be used with vitrified bonding systems without the significant decrease in abrading performance of conventional fused alumina-zirconia abrasive particles used with vitrified bonding systems.